In the typical manufacture of steel plate stock, a strip of steel material is unwound from a coil where it is flattened and fed through a shearing machine and cut to the desired length or the desired location. There are a variety of shears used by manufacturers including stationary shears and xe2x80x9cflyingxe2x80x9d shears. Stationary shears require the strip of material to stop for an instant while the shear makes each cut. Stopping the strip for a cut generally reduces the throughput of the operation. Flying shears are designed to cut the strip as it moves. There are several types of flying shears including rocking shears, oscillating shears, and drum shears. Because the shear moves to match the strip speed, flying shears can make an accurate cut without requiring the strip to stop and restart each time. This continuous flow greatly increases the productivity of process lines that perform a shearing operation. However, flying shears also have limitations making them unsuitable for many shearing applications. The rocking shear is mounted on a pivot shaft below the material. The shear rocks forward and matches the speed of the material during the cut, then rocks backward to repeat the process. While the rocking shear is generally the least expensive of the flying shears, its changing vertical cut angle limits it to relatively lighter gauges and slow speeds. The oscillating shear works much like a conventional stationary shear, with an additional frame that moves the knife holder frame to match the strip speed resulting in a clean vertical cut. While the oscillating shear generally produces a superior cut, it is the most expensive system and the required acceleration of the heavy knife holder frame limits it to slower speeds than the drum shears.
In a drum system, the cutting knives are typically mounted on a pair of drums. As the material passes between the drums, the knives meet and shear the material in two. There are a variety of types of drum shears including parallel cut drums and helical cut drums. The parallel cut types have straight knifes mounted parallel to the longitudinal axis of the drum. The parallel cut type drums are limited to the softer, lighter gauges due to the high force requirements necessary to make a simultaneous shear cut across the entire width of the material. The parallel cut rotary drum shears can provide good quality cutting at high speeds within these limitations.
The helical cut drum shears are generally not used for cut-to-length operations. With the helical cut drum shears, the knives are mounted along a helix angle on the drum. Accordingly, only one relatively small portion of the knife is shearing the material at one time as the drum rotates, resulting in significantly less force than typical parallel cut rotary drum shears. For example, a helical cut rotary drum having knives at a 5 degree helix angle may require only 10% of the cutting force required for a parallel cut. While this could reduce the equipment cost and provide significant savings for shearing applications, problems associated with the helical type drum shears make them generally unsuitable for cut-to-length operations. One such problem is that the knife cuts along a helix angle as the drums rotate, which creates an angled cut on the material. Cut-to-length operations typically require a squared cut perpendicular to the feed direction of the strip. Accordingly, the helical cutting drum shear is typically limited to scrap applications where angle of the cut is not important.
Accordingly, there exists a need in the art for a helical cutting type drum shear capable of providing a finish quality cut generally perpendicular or at a specific angle to the feed direction of the material.
The present invention overcomes at least one of the limitations of the prior art by providing an apparatus for cutting material moving at a first velocity. The apparatus comprises a means for cutting the material wherein the cutting means moves at a second velocity at a predetermined angle from the first velocity; and a means for moving the cutting means at a third velocity such that the combination of the second velocity and the third velocity is equivalent to the first velocity.